To install means to set something up in its proper place so it's ready to use. When you install a new app on your tablet, you're putting it onto your device and getting it ready to open. When workers install a ceiling fan, they attach it securely, connect the wires, and make sure it spins safely. Installing means making sure everything is connected, positioned, and working correctly. It involves careful setup and testing, not simply placing something somewhere.

You might install shelves in your bedroom, install a new battery in a toy, or install yourself in a comfortable chair with a good book (though this last use is more playful and old-fashioned).

Installation is the noun form: “The installation of the new playground equipment took two days.” When something is brand new and freshly set up, you might call it a new installation. In art museums, an installation is a special kind of artwork that's set up to fill an entire room or space, creating an experience you walk through rather than just look at.

The opposite is uninstall: removing something that was previously installed, like deleting an app you no longer need.